Regulation of metabolic pathways is accomplished through the control of enzymatic activities, explains Collin College. The cell accomplishes this by either altering a pre-existing enzyme's activity or changing the available amount of a particular enzyme, according to College of Saint Benedict and Saint John's University.
Changing the activity of another enzyme already in the cell is the fastest method of controlling an enzyme's activity, notes College of Saint Benedict and Saint John's University. Some strategies for accomplishing this include changing substrate availability and altering pH levels. Substrates are the reactants that bind to enzymes in certain amounts, measured in the unit Km. The cell is, thus, able to control the activity of a particular enzyme through modifying the amount of substrate available. When the amount of substrate available is significantly below the typical Km for that enzyme, its activity is lowered, and its activity is heightened when there is more substrate available than can bind with the enzyme.
Two ways of changing the concentration of an enzyme in a cell are degrading the messenger RNA, or mRNA, needed to produce the enzyme and post-translational changes, explains College of Saint Benedict and Saint John's University. Small inhibitor RNA molecules can attach to the mRNA of the particular enzyme, resulting in less of the enzyme being produced through translation. In other cases, changes are made after the enzymes are already translated to prevent them from reaching their active form.